Power generating plants, such as one operating a combined cycle power plant are well known for generating electricity. Combined cycle power plants use both gas and steam turbines. In such a plant, the power produced by a combustion turbine may be augmented by injecting steam or water into the gas flow path.
In general, the amount of power produced in the combustion turbine through such power augmentation is greater than the amount lost in the steam cycle due to the removal of steam. Power augmentation uses an appreciable quantity of steam generated from the heat recovery steam generator. When steam is removed for power augmentation, it is necessary to supply an equivalent amount of water as ‘make-up’ to the steam cycle. The make-up water is typically fully oxygenated in equilibrium with the oxygen in air. The concentration of oxygen in the make-up water is higher than that required in the feedwater to the heat recovery steam generator. Thus, there is a need to remove oxygen from the make-up water.
Removal of oxygen from make-up water for deaerating is typically accomplished by spraying the make-up water into a deaerator in the condenser then transferring the deaerated make-up water to a hotwell. In the deaerator, steam may be used to strip the oxygen from the water. At low make-up water flow volumes, low-pressure exhaust steam may be used for stripping in the deaerator. However, at higher make-up water flow volumes, low-pressure steam from the heat recovery steam generator may be required for the deaerator to function properly. Using low-pressure steam to deaerate higher flow volumes of make-up water may significantly reduce the steam turbine power output thereby reducing the overall efficiency of the power plant.